This invention relates to vacuum picks for handling semiconductor wafers, and more particularly, to a vacuum pick suitable for removing and inserting wafers in a cassette wafer holder.
In the fabrication of semiconductor devices, semiconductor wafers are subjected to a series of processing steps in individual processing systems such as ion implanters, thermal processors, sputtering systems, and etching systems. For each processing system it is necessary to introduce the wafers into the required processing position and then to remove the wafer after processing. For commercial processing systems, automated wafer handling has been used to increase throughput and reduce the contamination and damage associated with manual handling. As devices become smaller and more complex, the risk of defects from even micron size particles increases. It is, therefore, necessary that automated wafer handling devices not introduce contaminanation or damage the fragile wafers.
It has become standard in the semiconductor industry to store and transport semiconductor wafers in so-called cassettes wherein a plurality of wafers is stored upright in closely-spaced, facing alignment. The wafers can be accessed from above or below.
One prior art technique for removing wafers from cassettes involves positioning the cassette vertically with the wafers horizontally oriented and utilizing a pair of moving belts to remove wafers one at a time as the cassette is indexed vertically. This arrangement has the disadvantage that the horizontally-oriented wafers can collect particulate contamination on their upper surface. In addition, the belt system cannot access wafers randomly in the cassette, but must start at one end and successively remove each wafer until all are removed.
In another technique for handling wafers in a cassette, a wafer lift blade, having a leading edge which is curved and grooved to accommodate the wafer edge, accesses wafers from below and lifts them vertically to a processing station. This edgewise handling technique can access wafers randomly in the cassette and has proven generally satisfactory. However, edge handling results in some abrasion and generation of particulates.
Vacuum picks have also been utilized for handling of semiconductor wafers. Typically, the rear surface of the wafer is held to the support surface of a vacuum pick by vacuum suction. However, vacuum picks have not been used for direct removal of wafers from cassettes due to the uncertainty in wafer position, tipping of the wafer in its slot, and tolerances in the cassette itself. These factors make it difficult to reliably remove and replace wafers in a cassette without damage to adjacent wafers.
It is a general object of the present invention to provide a novel vacuum pick for handling of thin, disk-like workpieces.
It is another object of the present invention to provide a novel vacuum pick for accessing closely-spaced semiconductor wafers.
It is still another object of the present invention to provide a novel vacuum pick which has a flexible workpiece gripping means to compensate for variations in workpiece position.